It is known to produce printing image deposits on the surface of a lithographic printing member and fix such printing image deposits by the application of heat. In addition, it is known to remove such printing image deposits from such lithographic printing member surfaces at the conclusion of the printing run. Such a process is disclosed in Canadian Patent 1,075,300 of Wright. The Wright disclosure refers to electrostatographic recording to produce a printing image deposit on an electrostatographic recording member, which printing image deposit is subsequently transferred to the surface of a lithographic printing member and heat-fixed thereto. At the completion of the printing run the printing image deposit is removed from the lithographic printing member surface by the combined action of a solvent and friction.
The process of the Wright disclosure has certain disadvantages, of which the most significant is the image removal step, which involves the combined use of a suitable solvent and friction. This is a laborious and time-consuming process which can alter the grain structure of the lithographic surface and affect seriously its water accepting properties. In addition, when such an operation is carried out on-line on the printing press, care must be taken to confine the solvent to the printing member surface and in particular to avoid contamination of the printing ink in the ink fountain of the press. The solvents used are generally environmentally objectionable and some are highly inflammable.
In addition to the foregoing, the usual prior art heat fusion process requires placing of the printing plate in an oven at a suitably raised temperature for a finite time. Such a process step is not suited to an on-line operation, in which instance a heating mantle or similar device may be used to heat the image deposit and fuse such deposit to the surface of the lithographic printing plate. Each of these methods tends primarily to cause coherence of the printing deposit rather than adhesion of the printing deposit to the plate surface.